I'd hate for the sentient/controlled armor scenes to be dream sequences --- that's lame, and even lamer to try to drum up hype for dream sequences in a trailer. It's bait 'n' switch.

No, M-2's theory makes the most sense to me now: Tony gets the Extremis tech from Killian, thinking it's the Next Big Thing; but unbeknownst to Stark, the Extremis armor can be remotely controlled by Mandarin. The "nightmare" sequence involves Mandarin powering up the Extremis armor to go wandering around and scout out Stark's mansion in the middle of the night, and when he spots Pepper there, he moves the armor in for a closer look....

But I still think the Sentient Armor angle can be worked in, as that might be Stark's initial reaction to the situation --- he thinks the tech is so advanced that it's become self-aware, when in actuality it's simply being manipulated from afar by Mandarin.

After watching the trailer again, I have to say I kinda like the sentient armor angle.

That scene with the armor pulling Pepper could easily be the armor trying to warn her about something.

If u look at the scene where the armor is on top of Tony, you will notice the house is crumbling and Tony has the same shirt he has on when him and Pepper see the helicopters coming. So it could be that the armor assembles itself and basically saves Tony, by allowing Tony to put it on.